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Old 06-25-2013, 11:05 PM
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Dual chamber master cylinder plumbing

I would like to replace the single chamber master cylinder on my '57 D100 with a dual chamber master cylinder.

I am thinking that the plumbing should be front->opposite side rear to each chamber. My thinking is that if I lose a brake line, I would have a wheel at each end and opposite each other to help get me to a stop in a fairly straight line.

Right front - left rear plumbed together
Left front - right rear plumbed together

Thoughts?

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Old 06-25-2013, 11:39 PM
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Quote:
Originally Posted by 57DodgePU View Post
I would like to replace the single chamber master cylinder on my '57 D100 with a dual chamber master cylinder.

I am thinking that the plumbing should be front->opposite side rear to each chamber. My thinking is that if I lose a brake line, I would have a wheel at each end and opposite each other to help get me to a stop in a fairly straight line.

Right front - left rear plumbed together
Left front - right rear plumbed together

Thoughts?
If you have a master Cylinder with four ports on it..You only need to use two ports..On one side or the other,,One for the front and one for the back... You don't use all four.. If I'm reading you right..

Your two fronts are off one port,,, Your two back's are off one port... If you lose a line front or back you will still have brakes..
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Old 06-26-2013, 04:41 AM
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Do NOT, and I repeat NOT, cross up your brake lines like you suggested. You will want front OR back to stop the truck in a straight line during an emergency or loss of a line on either end. Crossing the brake lines like you suggested is very dangerous and could cause loss of control during panick braking or wet conditions. Brake bias, different tire sizes and even steering the car during hard braking will cause all sorts of mayhem. ALWAYS plumb the fronts to one reservoir and the rears to another.
Mark
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Old 06-26-2013, 04:49 AM
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Originally Posted by astroracer View Post
Do NOT, and I repeat NOT, cross up your brake lines like you suggested. You will want front OR back to stop the truck in a straight line during an emergency or loss of a line on either end. Crossing the brake lines like you suggested is very dangerous and could cause loss of control during panick braking or wet conditions. Brake bias, different tire sizes and even steering the car during hard braking will cause all sorts of mayhem. ALWAYS plumb the fronts to one reservoir and the rears to another.
Mark
ditto. you'll need a brake proportioning valve also. and they are different if all disc or disc/drum compo..
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Old 06-26-2013, 08:05 AM
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Thank you for the information. The truck has drums all the way around and will have same size tires all the way around.

Fronts and backs only; no cross-connecting.
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Old 06-26-2013, 09:39 AM
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Quote:
Originally Posted by 57DodgePU View Post
Thank you for the information.
Too bad much of it is incorrect. First, DO NOT use a proportioning valve with a drum/drum system. You only need one for a system with discs.

Second, the cross-connecting you talk about is called dual diagonal braking, and many cars are plumbed that way. Your rationale for doing it is spot on. Until the mid-1980s, it was really only done on foreign cars, but domestics have adopted it. My 1990 Grand Am (which does NOT have antilock brakes, in case anyone asks) has a dual diagonal system. Since it has discs front and drums rear, it has two proportioning valves, one in each half of the system. Your drum/drum system would not need that.

Bottom line is that you can plumb your either way, front/back or dual diagonal. The only reason not to do the diagonal system is if your truck used a load sensing valve on the rear brakes, which I'm sure it does not.
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Old 06-26-2013, 09:59 AM
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Quote:
Originally Posted by joe_padavano View Post
Too bad much of it is incorrect. First, DO NOT use a proportioning valve with a drum/drum system. You only need one for a system with discs.

Second, the cross-connecting you talk about is called dual diagonal braking, and many cars are plumbed that way. Your rationale for doing it is spot on. Until the mid-1980s, it was really only done on foreign cars, but domestics have adopted it. My 1990 Grand Am (which does NOT have antilock brakes, in case anyone asks) has a dual diagonal system. Since it has discs front and drums rear, it has two proportioning valves, one in each half of the system. Your drum/drum system would not need that.

Bottom line is that you can plumb your either way, front/back or dual diagonal. The only reason not to do the diagonal system is if your truck used a load sensing valve on the rear brakes, which I'm sure it does not.
in todays world. a drum drum system NEEDS a proportioning valve . as the ole systems locked up the rears WAY TO EARLY.. YES you don't need it.. but if you plan on being somewhat safe and bring the all drum set up to better stopping so you have a fighting chance if a newer car stops on a dime. you'll want a proportioning valve to bleed off some pressure to the rears and let the fronts do 70% of the stopping..
most cars JOE says has the dual diagonal system are also almost equal weight front to rear. and the BRAKES themselves are balanced in swept area to use it set up that way.. a truck is not even close to being equal weight front to rear. and your brakes swept area wasn't designed for it either. hook it up that way and you'll swap ends under braking in the rain or sand/etc..
good luck
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Old 06-26-2013, 10:04 AM
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Quote:
Originally Posted by joe_padavano View Post
Too bad much of it is incorrect. First, DO NOT use a proportioning valve with a drum/drum system. You only need one for a system with discs.

Second, the cross-connecting you talk about is called dual diagonal braking, and many cars are plumbed that way. Your rationale for doing it is spot on. Until the mid-1980s, it was really only done on foreign cars, but domestics have adopted it. My 1990 Grand Am (which does NOT have antilock brakes, in case anyone asks) has a dual diagonal system. Since it has discs front and drums rear, it has two proportioning valves, one in each half of the system. Your drum/drum system would not need that.

Bottom line is that you can plumb your either way, front/back or dual diagonal. The only reason not to do the diagonal system is if your truck used a load sensing valve on the rear brakes, which I'm sure it does not.
Well shut my mouth!!! Thanks Joe! For all of the work I do designing suspensions I have never really delved into the design and workings of a typical brake system.
My apologies to the OP on the mis-information... I had no idea this was being done! It just seems wrong to me initially but I guess it works well if all of the OEM's have gone this way...

I found this on Wiki:
"Diagonal split systems were used initially on American Motors automobiles in the 1967 production year. The right front and left rear are served by one actuating piston while the left front and the right rear are served, exclusively, by a second actuating piston (both pistons pressurize their respective coupled lines from a single foot pedal). If either circuit fails, the other, with at least one front wheel braking (the front brakes provide most of the speed reduction) remains intact to stop the mechanically-damaged vehicle. Just before 1970, diagonally split systems had become universal for automobiles sold in the United States. This system was developed with front wheel drive cars suspension design to maintain better control and stability during a system failure.

The diameter and length of the master cylinder has a significant effect on the performance of the brake system. A larger diameter master cylinder delivers more hydraulic fluid to the caliper pistons, yet requires more brake pedal force and less brake pedal stroke to achieve a given deceleration. A smaller diameter master cylinder has the opposite effect.

A master cylinder may also use differing diameters between the two sections to allow for increased fluid volume to one set of caliper pistons or the other.
"
I have not plumbed the lines on my van build but this will give me something to look into before I do. I am using an Astro Hydro boost unit and I don't know if the vans wire plumbed front/rear or Diagonally.
Mark
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Old 06-26-2013, 11:18 AM
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problems with believing that, if since 1970 the systems was split one front one rear, then the master fuild areas would be equal and they are not. and car with disc/drum the drums have half the fuild aval. than the discs..
I've lost breaks in a 1970 chevelle only had rears fronts leaked/popped
1983 s-10 lost rears only had both fronts..
1980 t/a loose rears (slowly) if you held the pedal it slowly sink and you'd have only fronts, great for burnouts.
so I'm not buy'n any of this..
went out to my 1971 truck and 86 monte SS and 84 indy and not one has a system with a split one rear&1 front tied together.
think that wiki needs work.
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Old 06-26-2013, 11:23 AM
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crack the line at the master on a car say the bigger fluid end. do you loose both fronts or one of each(1front one rear) nope you loose both fronts.. if it was plumbed in the proportioning valve then cracking the front line on the dual master would only kill half of the braking at all 4 wheels..
and if the meteringblock/proportioning valve split the brakes front/rear one each. then you'd only need one pod master..

ABS is a whole other story. and that's not what he'd(o/p) be dealing with as abs can run as 4 separate systems if one line breaks(left rear) you'll still have brakes at the other 3 wheels on a 4 channel abs.
3 channel, the rears are tied together..
that wiki needs work from an ASA brake master tech as it's not correct at all
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Old 06-26-2013, 12:04 PM
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Quote:
Originally Posted by gearheadslife View Post
most cars JOE says has the dual diagonal system are also almost equal weight front to rear.
A FWD 1990 Grand Am does NOT have anywhere near 50-50 weight distribution, especially with the iron V6. Saabs and Volvos, also FWD and nowhere near 50-50, have had dual diagonal braking since the 1960s.

Quote:
crack the line at the master on a car say the bigger fluid end. do you loose both fronts or one of each(1front one rear) nope you loose both fronts.
OBVIOUSLY, any vehicle with different sized M/C reservoirs does NOT have a diagonally-split braking system. I take Wikipedia with a grain of salt, since there's a lot on it that is also incorrect, like the quoted passage about American cars going to diagonal split systems in the 1970s. That is not true, and if you read my previous post, I said GM STARTED changing in the late 1980s, BEFORE ABS was common. I know from owing one that the N-body cars have them, as did the Cadillac Allantes. I also know that my 86 Caprice (designed in the mid-1970s) wagon does not, nor does my 86 Chevy one ton (designed in the EARLY 1970s). Just about every GM passenger car DESIGNED since the mid-80 does have a diagonally split system.

More to the point, while a diagonally split system may or may not be the right choice for the OP, I'm really reacting to absolute statements like this:

Quote:
Do NOT, and I repeat NOT, cross up your brake lines like you suggested.
Never say never.
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Old 06-26-2013, 04:43 PM
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Yea, I did a bit of a knee jerk on that when I found it. I have done a lot more research and find that the Front Wheel Drive cars will generally have some type of split braking set-up. Not that they all do but I am seeing it used mostly on the FWD's. The heavier weight bias to the front makes sense to have at least one caliper working up there at all times.
I will go back to my original statement to the OP that he wants to stick with a Front/Rear system for his Rear Wheel Drive, Drum brake pick-up.
Mark

P.S. - I concider myself a little bit wiser because of this thread. Thanks OP, thanks Joe.
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Old 06-26-2013, 07:16 PM
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Well I will say this....Not sure what you are calling wrong here,,, But it's turnning more wrong as it goes... A master Cylinder with four ports on it is to use what every side you want to.. One line goes to the front and tee's off to both wheels,,, The other port goes to the back and tee's off to both wheels...Now you should run an adjustable proportioning valve in the back line...

Running off both front and back ports is a waste of time and money on extra brake lines... And you end up with the same thing as if you tied into the lines on one side... Both front ports are tied together and also the back... If you lose one side tied into both fronts.. You still lose both fronts..

Really funny how some people post here..


Yes on a new car there is a bunch of brake lines that isn't needed... Along with a bunch of wires, A bunch of vacuum lines, And a bunch of other ******* that isn't really needed..
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Old 06-27-2013, 08:18 AM
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This has been a very lively and interesting conversation with tons of information. I really appreciate all of the input and helping me understand the pros / cons of my thoughts of the master cylinder plumbing.

More?
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Old 06-27-2013, 08:31 AM
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Thank You as well... The only thing I was getting at is,, I'm thinking this is going in your 57 model truck,,,If so,, I don't think you will be having the same set up as a say 2000 model truck,, When doing a older car or truck the brakes can be run a little different then the new cars of today,, No ABS, Or the other crap,, Brakes can be ran very simple and safe,, And work just as good... If you want to go by todays book's,, You will have all kind of lines ran under your hood for no better reason what so ever..
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